U.S. patent application number 13/685441 was filed with the patent office on 2014-05-29 for crack resistant solar cell modules.
This patent application is currently assigned to SUNPOWER CORPORATION. The applicant listed for this patent is Sunpower Corporation. Invention is credited to Nicholas BOITNOTT, Sung Dug KIM.
Application Number | 20140144487 13/685441 |
Document ID | / |
Family ID | 50772197 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140144487 |
Kind Code |
A1 |
KIM; Sung Dug ; et
al. |
May 29, 2014 |
CRACK RESISTANT SOLAR CELL MODULES
Abstract
A crack resistant solar cell module includes a protective
package mounted on a frame. The protective package includes a
polyolefin encapsulant that protectively encapsulates solar cells.
The polyolefin has less than five weight percent of oxygen and
nitrogen in the backbone or side chain. In other words, the
combined weight percent of oxygen and nitrogen in any location in
the molecular structure of the polyolefin is less than five. The
polyolefin also has a complex viscosity less than 10,000 Pa second
at 90.degree. C. as measured by dynamic mechanical analysis (DMA)
before any thermal processing of the polyolefin. The protective
package includes a top cover, the encapsulant, and a backsheet. The
solar cell module allows for shipping, installation, and
maintenance with less risk of developing cracks on the surfaces of
the solar cells.
Inventors: |
KIM; Sung Dug; (Pleasanton,
CA) ; BOITNOTT; Nicholas; (San Francisco,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sunpower Corporation; |
|
|
US |
|
|
Assignee: |
SUNPOWER CORPORATION
SAN JOSE
CA
|
Family ID: |
50772197 |
Appl. No.: |
13/685441 |
Filed: |
November 26, 2012 |
Current U.S.
Class: |
136/251 ;
438/66 |
Current CPC
Class: |
B32B 27/36 20130101;
H01L 31/0481 20130101; Y02B 10/12 20130101; B32B 27/365 20130101;
B32B 2307/412 20130101; B32B 27/32 20130101; B32B 2457/00 20130101;
B32B 27/304 20130101; Y02B 10/10 20130101; H01L 31/18 20130101;
B32B 27/322 20130101; H01L 31/1876 20130101; B32B 27/08 20130101;
H01L 31/048 20130101; Y02E 10/50 20130101 |
Class at
Publication: |
136/251 ;
438/66 |
International
Class: |
H01L 31/048 20060101
H01L031/048; H01L 31/18 20060101 H01L031/18 |
Claims
1. A solar cell module comprising: a plurality of solar cells; an
encapsulant encapsulating the plurality of solar cells, the
encapsulant comprising polyolefin having less than 5 weight percent
oxygen and nitrogen in a backbone or side chain, the polyolefin
having a complex viscosity less than 10,000 Pa-s at 90.degree. C.
as measured by dynamic mechanical analysis before any thermal
processing of the encapsulant; a transparent top cover on a front
portion of the solar cell module, the front portion facing the sun
during normal operation; and a backsheet on a back portion of the
solar cell module.
2. The solar cell module of claim 1 wherein the polyolefin has a
volume resistivity of at least 10.sup.15 Ohm-cm as measured by ASTM
D257 test at 1 kV, 10 min electrification, and 60.degree. C.
3. The solar cell module of claim 1 further comprising: a frame,
and wherein the transparent top cover, the encapsulant
encapsulating the plurality of solar cells, and the backsheet are
mounted on the frame.
4. The solar cell module of claim 3 wherein the plurality of solar
cells are electrically isolated from the frame.
5. The solar cell module of claim 1 wherein the plurality of solar
cells comprises backside contact solar cells.
6. The solar cell module of claim 1 wherein the polyolefin
comprises polyethylene.
7. The solar cell module of claim 1 wherein the polyolefin
comprises polypropylene.
8. A method of manufacturing a solar cell module, the method
comprising: providing an encapsulant for a solar cell module, the
encapsulant comprising polyolefin having less than five weight
percent of oxygen and nitrogen in a backbone or side chain, and
having a complex viscosity that is less than 10,000 Pascal second
at 90.degree. C. as measured by dynamic mechanical analysis before
protectively packaging a plurality of solar cells in the
encapsulant to create a protective package; protectively packaging
the plurality of solar cells in the encapsulant to create the
protective package; and mounting the protective package on a
frame
9. The method of claim 8 wherein the polyolefin has a volume
resistivity of at least 10.sup.15 Ohm-cm as measured by ASTM D257
test at 1 kV, 10 min electrification, and 60.degree. C.
10. The method of claim 8 wherein the plurality of solar cells
comprises backside contact solar cells.
11. The method of claim 8 wherein the polyolefin comprises
polyethylene.
12. The method of claim 8 wherein the polyolefin comprises
polypropylene.
13. The method of claim 8 wherein protectively packaging the
plurality of solar cells in the encapsulant to create the
protective package comprises: placing the plurality of solar cells
between a top sheet and a bottom sheet of the encapsulant, a
backsheet under the bottom sheet of the encapsulant, and a
transparent top cover over the top sheet of the encapsulant; and
pressing and heating together the top and bottom sheets of the
encapsulant, the top cover, and the backsheet.
14. The method of claim 13 wherein the top and bottom sheets of the
encapsulant, the top cover, and the backsheet are pressed and
heated together by vacuum lamination.
15. A solar cell module comprising: a plurality of solar cells; a
protective package comprising an encapsulant that encapsulates the
plurality of solar cells, the encapsulant comprising polyolefin
having less than 5 weight percent oxygen and nitrogen in a backbone
or side chain; and a frame on which the protective packaging is
mounted.
16. The solar cell module of claim 15 wherein the polyolefin has a
complex viscosity less than 10,000 Pa-s at 90.degree. C. as
measured by dynamic mechanical analysis before any thermal
processing of the encapsulant.
17. The solar cell module of claim 15 wherein the polyolefin has a
volume resistivity of at least 10.sup.15 Ohm-cm as measured by ASTM
D257 test at 1 kV, 10 min electrification, and 60.degree. C.
18. The solar cell module of claim 15 wherein the protective
packaging comprises: a transparent top cover; the encapsulant
encapsulating the plurality of solar cells; and a backsheet.
19. The solar cell module of claim 15 wherein the polyolefin
comprises polyethylene.
20. The solar cell of claim module of claim 15 wherein the
polyolefin comprises polypropylene.
Description
TECHNICAL FIELD
[0001] Embodiments of the subject matter described herein relate
generally to solar cell modules. More particularly, embodiments of
the subject matter relate to solar cell module structures and
manufacturing processes.
BACKGROUND
[0002] Solar cells are well known devices for converting solar
radiation to electrical energy. A solar cell has a front side that
faces the sun during normal operation to collect solar radiation
and a backside opposite the front side. Solar radiation impinging
on the solar cell creates electrical charges that may be harnessed
to power an external electrical circuit, such as a load.
[0003] Solar cells may be serially connected and packaged together
to form a solar cell module. The packaging provides environmental
protection for the solar cells. Prior to operation in the field,
such as in a residential home, commercial structure, or
photovoltaic power plant, solar cell modules may be subjected to
rough handling during shipping, installation, and maintenance.
Embodiments of the present invention pertain to solar cell modules
with features that prevent cracks from developing on solar
cells.
BRIEF SUMMARY
[0004] In one embodiment, a crack resistant solar cell module
includes a protective package mounted on a frame. The protective
package includes a polyolefin encapsulant that protectively
encapsulates solar cells. The polyolefin has less than five weight
percent of oxygen and nitrogen in the backbone or side chain. In
other words, the combined weight percent of oxygen and nitrogen in
any location in the molecular structure of the polyolefin is less
than five. The polyolefin also has a complex viscosity less than
10,000 Pa second at 90.degree. C. as measured by dynamic mechanical
analysis (DMA) before any thermal processing (e.g., lamination) of
the polyolefin. The protective package includes a top cover, the
encapsulant, and a backsheet. The solar cell module allows for
shipping, installation, and maintenance with less risk of
developing cracks on the surfaces of the solar cells.
[0005] These and other features of the present invention will be
readily apparent to persons of ordinary skill in the art upon
reading the entirety of this disclosure, which includes the
accompanying drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] A more complete understanding of the subject matter may be
derived by referring to the detailed description and claims when
considered in conjunction with the following figures, wherein like
reference numbers refer to similar elements throughout the figures.
The figures are not drawn to scale.
[0007] FIG. 1 schematically shows a plan view of a portion of an
example solar cell module with fern cracks.
[0008] FIG. 2 shows a perspective view of a solar cell module in
accordance with an embodiment of the present invention.
[0009] FIGS. 3-5 are cross-sectional views schematically
illustrating a method of making a solar cell module in accordance
with an embodiment of the present invention.
[0010] FIG. 6 shows a flow diagram of a method manufacturing a
solar cell module in accordance with an embodiment of the present
invention.
DETAILED DESCRIPTION
[0011] In the present disclosure, numerous specific details are
provided, such as examples of components, materials, and methods,
to provide a thorough understanding of embodiments of the
invention. Persons of ordinary skill in the art will recognize,
however, that the invention can be practiced without one or more of
the specific details. In other instances, well-known details are
not shown or described to avoid obscuring aspects of the
invention.
[0012] FIG. 1 schematically shows a plan view of a portion of an
example solar cell module 150 with fern cracks. The solar cell
module 150 includes a plurality of solar cells 151 (i.e., 151-1,
151-2, 151-3, 151-4, etc.) that are mounted on a frame 152. There
are many solar cell modules 151 in the solar cell module 150, but
only some in the upper left corner are shown for clarity of
illustration.
[0013] In general, solar cell modules are shipped from their
source, such as a warehouse or factory, to the job site where the
solar cell modules will be installed and operated. The solar cell
modules may be subjected to rough handling as they are loaded and
unloaded during shipment. At the job site, the solar cell modules
may be subjected to further rough handling before or during
installation and during maintenance. For example, prior to
installation, the solar cell modules may be left on the floor where
they may be stepped on by installers and other workers. Some
installers may also ignore proper handling instructions.
[0014] In the example of FIG. 1, some of the solar cells 151 have
fern cracks 152. The fern cracks 152 may be caused by rough
handling and repeated mechanical stress in the field. The fern
cracks 152 are so named because they usually, but not necessarily,
branch out and extend on the surface of the damaged solar cell 151.
In the example of FIG. 1, the solar cells 151-1, 151-2, and 151-4
(but not the solar cell 151-3) have fern cracks 152. The fern
cracks 152 may induce hot solar cells and may result in power
loss.
[0015] Referring now to FIG. 2, there is shown a perspective view
of a solar cell module 100 in accordance with an embodiment of the
present invention. The solar cell module 100 is a so-called
"terrestrial solar cell module" in that it is designed for use in
stationary applications, such as on rooftops or by photovoltaic
power plants. In the example of FIG. 2, the solar cell module 100
includes an array of interconnected solar cells 101. Only some of
the solar cells 101 are labeled in FIG. 2 for clarity of
illustration. In the example of FIG. 2, the solar cells 101
comprise backside contact solar cells. In a backside contact solar
cell, all diffusion regions and metal contacts coupled to the
diffusion regions are formed on the backside of the solar cell.
That is, both the P-type and N-type diffusion regions and metal
contacts coupled to them are on the backside of the solar cell. In
other embodiments, the solar cells 101 comprise front contact solar
cells where one polarity of diffusion regions (e.g., N-type
diffusion regions) are on the front side of the solar cells, and
the opposite polarity of diffusion regions (e.g., P-type diffusion
regions) are on the backside of the solar cells.
[0016] Visible in FIG. 2 are the front sides of the solar cells
101. The front sides of the solar cells 101 are also referred to as
the "sun side" because they face towards the sun during normal
operation. The backsides of the solar cells 101 are opposite the
front sides. A frame 102 provides mechanical support for the solar
cells 101. The front portion 103 of the solar cell module 100 is on
the same side as the front sides of the solar cells 101 and is
visible in FIG. 2. The back portion 104 of the solar cell module
100 is under the front portion 103. The back portion 104 of the
solar cell module 100 is on the same side as the backsides of the
solar cells 101.
[0017] FIGS. 3-5 are cross-sectional views schematically
illustrating a method of making a solar cell module 100 in
accordance with an embodiment of the present invention.
[0018] FIG. 3 is an exploded view showing the components of the
solar cell module 100 in accordance with an embodiment of the
present invention. The solar cell module 100 may comprise a
transparent top cover 251, sheets of encapsulant 252, the solar
cells 101, interconnects 254, and a backsheet 253. The sheet of
encapsulant 252 on the front portion 103 is labeled as "252-1" and
the sheet of encapsulant 252 on the back portion 104 is labeled as
"252-2." The transparent top cover 251 and the front side
encapsulant 252-1 serve as front side packaging components, and the
backside encapsulant 252-2 and the backsheet 253 serve as backside
packaging components. In the example of FIG. 3, the transparent top
cover 251 is the outermost front side packaging component and the
backsheet 253 is the outermost backside packaging component.
[0019] The transparent top cover 251 and the encapsulant 252
comprise optically transparent materials. The transparent top cover
251, which is the topmost layer on the front portion 103, protects
the solar cells 101 from the environment. The solar cell module 100
is installed in the field such that the transparent top cover 251
faces the sun during normal operation. The front sides of the solar
cells 101 face towards the sun by way of the transparent top cover
101. In the example of FIG. 3, the transparent top cover 201
comprises glass (e.g., 3.2 mm thick, soda lime glass).
[0020] The encapsulant 252 protectively encapsulates the solar
cells 101. The inventors discovered that there is a correlation
between fern cracks and the type of encapsulant employed. At the
material level, the inventors also discovered that the viscosity of
the encapsulant is critical to control the degree or severity of
the fern crack. These discoveries are unexpected in that the
characteristics of the encapsulant, instead of the solar cells
themselves, need to be addressed to mitigate fern cracks on the
solar cells. In embodiments of the present invention, the
characteristics of the encapsulant 252 are optimized to reduce
occurrence of fern cracks on the solar cells 101.
[0021] In one embodiment, the encapsulant 252 comprises polyolefin.
Examples of suitable polyolefin include polyethylene, high density
polyethylene, low density polyethylene, linear low density
polyethylene, and polypropylene. In one embodiment, to guard
against fern cracks, the encapsulant 252 comprises polyolefin that
has less than 5 weight percent of oxygen and nitrogen in the
backbone or side chain. In other words, the combined weight percent
of oxygen and nitrogen in any location in the molecular structure
of the polyolefin is less than five. In one embodiment, the
polyolefin further has a complex viscosity less than 10,000 Pa-s
(Pascal second) at 90.degree. C. as measured by dynamic mechanical
analysis (DMA) before lamination or any other thermal processing.
The volume resistivity of the polyolefin of the encapsulant 252 is
preferably at least 10.sup.15 Ohm-cm as measured by ASTM D257 test
at 1 kV, 10 min electrification, and 60.degree. C. As is well
known, ASTM D257 is a standard by ASTM International, which is
formerly known as the American Society for Testing and
Materials.
[0022] The interconnects 254 may comprise a metal for electrically
interconnecting the solar cells 101. In the example of FIG. 3, the
solar cells 101 comprise serially-connected backside contact solar
cells, and the interconnects 254 electrically connect to
corresponding P-type and N-type diffusion regions on the backsides
of the solar cells 101. The solar cells 101 may also comprise
serially-connected front contact solar cells, in which case the
interconnects 254 would connect to diffusion regions on the
backside and front side of the solar cells.
[0023] The backsides of the solar cells 101 face the backsheet 253.
The backsheet 253 may be any single layer or multiple layers of
materials that provide environmental protection to other components
of the solar cell module 100. For example, flouropolymer,
polyvinylidene fluoride, polytetrafluoroethylene, polypropylene,
polyphenylene sulfide, polyester, polycarbonate, or polyphenylene
oxide may be used as a single layer or as part of multiple layers
of backsheet. The backsheet 253 is on the back portion 104.
[0024] In one embodiment, the transparent top cover 251, the
encapsulant 252-1 on the front side, the solar cells 101
electrically connected by the interconnects 254, the encapsulant
252-2 on the backside, and the backsheet 253 are formed together to
create a protective package. This is illustrated in FIG. 4, where
the aforementioned components are formed together in the stacking
order of FIG. 3. More particularly, the solar cells 101 are placed
between the encapsulants 252-1 and 252-2, the backsheet 253 is
placed under the encapsulant 252-2, and the transparent top cover
251 is placed over the encapsulant 252-1. The just mentioned
components are then pressed and heated together by vacuum
lamination, for example. The lamination process melts together the
sheet of encapsulant 252-1 and the sheet of encapsulant 252-2 to
encapsulate the solar cells 101. In FIG. 4, the encapsulant 252-1
and the encapsulant 252-2 are simply labeled as "252" to indicate
that that they have been melted together.
[0025] FIG. 5 shows the protective package of FIG. 4 mounted on the
frame 102. Being encapsulated in the encapsulant 252, the solar
cells 101 are electrically isolated from the frame 102.
[0026] Tables 1, 2, and 3 discussed below show the effectiveness of
the above disclosed encapsulants in preventing fern cracks.
[0027] Table 1 shows the complex viscosity of various polyolefin
encapsulants (Sample 1, Sample 2, Sample 3, and Sample 4) at
various temperatures measured at 1/s shear rate by dynamic
mechanical analysis. Table 1 shows complex viscosity in Pascal
second (Pa-s). The viscosities were measured before any thermal
processing of the encapsulants, which in this example is before
lamination.
TABLE-US-00001 TABLE 1 Temperature (.degree. C.) Sample 1 Sample 2
Sample 3 Sample 4 50 7.0E+04 8.3E+04 9.5E+03 8.4E+04 90 2.9E+04
4.1E+04 2.4E+03 7.3E+03 130 1.6E+04 4.7E+03 1.6E+03 2.3E+03 140
1.5E+04 4.3E+03 1.5E+03 2.3E+03 150 1.3E+04 3.3E+03 1.5E+03
2.3E+03
[0028] As shown in Table 1, the polyolefin encapsulants referred to
as "Sample 3" and "Sample 4" have a complex viscosity less than
10,000 Pa-s at 90.degree. C. Samples 3 and 4 have the
characteristics of encapsulants in accordance with embodiments of
the present invention. The polyolefin encapsulants referred to as
"Sample 1" and "Sample 2" have complex viscosities greater than
10,000 Pa-s at 90.degree. C., and therefore do not have the
characteristics for preventing fern cracks.
[0029] Table 2 shows the relative probability of developing fern
cracks on the solar cells when using the above-noted samples of
polyolefin encapsulants. More particularly, as noted in Table 2,
studies performed by the inventors indicate that solar cells
encapsulated by Sample 1 are four times more likely to develop
cracks compared to solar cells encapsulated by Sample 3. Similarly,
solar cells encapsulated by Sample 2 are three times more likely to
develop cracks compared to solar cells encapsulated by Sample
3.
TABLE-US-00002 TABLE 2 Relative Probability of Cracking Cell Sample
1 4x Sample 2 3x Sample 3 1x (baseline)
[0030] Table 3 shows relative power degradation of solar cells
encapsulated by Sample 2, Sample 3, and Sample 4 in a stress test
where a person stepped on the solar cell modules. The stress test
simulates foot traffic during installation or cleaning process in
the field. A person weighing 85 kg stepped on all of the solar
cells of the module in the first test. In a second test, a person
weighing 120 kg stepped on all of the solar cells of the
module.
TABLE-US-00003 TABLE 3 Relative power Relative power degradation
for degradation for 85 kg 120 kg person person stepping on stepping
on solar solar cell module cell module Sample 2 5.7x 15x Sample 3
1x (baseline) 1x (baseline) Sample 4 0.6x 0.6x
[0031] As shown in Table 3, solar cells encapsulated by Sample 2
exhibited much higher power degradation compared to solar cells
encapsulated by either Sample 3 or Sample 4. The difference in
relative power degradation of the solar cells increased when a
heavier person walked on the solar cell modules.
[0032] FIG. 6 shows a flow diagram of a method of manufacturing a
solar cell module in accordance with an embodiment of the present
invention. The method of FIG. 6 includes providing an encapsulant
for a solar cell module (step 301). In one embodiment, the
encapsulant comprises polyolefin having less than five weight
percent of oxygen and nitrogen in the backbone or side chain, and
having a complex viscosity that is less than 10,000 Pascal second
at 90.degree. C. as measured by dynamic mechanical analysis before
lamination or any thermal processing. The polyolefin encapsulant
may also have a volume resistivity of at least 10.sup.15 Ohm-cm as
measured by ASTM D257 test at 1 kV, 10 min. electrification, and
60.degree. C.
[0033] Solar cells to be included in the solar cell module are
protectively packaged in the encapsulant (step 302). In one
embodiment, the solar cells are placed between sheets (e.g., a
bottom sheet and a top sheet) of the encapsulant, a backsheet is
placed under a bottom sheet of the encapsulant, and a transparent
top cover is placed over a top sheet of the encapsulant. The
transparent top cover, the solar cells sandwiched by the sheets of
the encapsulant, and the backsheet are then pressed and heated
together by vacuum lamination, for example. The resulting
protective package is then mounted on a frame (step 303). The
manufactured solar cell module is resistant to fern cracks,
reducing the chance of damaging the solar cells contained therein
during shipping, installation, and maintenance.
[0034] Crack resistant solar cell modules and method of
manufacturing same have been disclosed. While specific embodiments
of the present invention have been provided, it is to be understood
that these embodiments are for illustration purposes and not
limiting. Many additional embodiments will be apparent to persons
of ordinary skill in the art reading this disclosure.
* * * * *